1. Field of the Invention
The present invention relates to a liquid supplying apparatus, a liquid ejecting apparatus, and a pressure control method, and in particular, relates to a pressure control technique related to liquid used for an inkjet head.
2. Description of the Related Art
With an ink supplying system which performs back-pressure control by feeding of ink in an inkjet recording apparatus, variances in a performance of a pump for pressurizing ink may potentially cause the ink supplying system to lose its ability to appropriately control pressure and control ink feeding. In particular, when a tube pump is applied as the pump used for ink feeding, such a loss in ability may be caused not only by variances in initial performance attributable to variances in size of parts used in the tube pump, an assembly variance of the tube pump, and a variance in an elasticity of a tube used for the tube pump, but also by a change over time in the elasticity of the tube.
In consideration of such problems, Japanese Patent Application Publication No. 2000-229422 discloses an inkjet recording apparatus including a first sensor which determines a number of revolutions of a motor used to drive a pump and a second sensor which measures a pressure of ink supplied to a head, wherein the inkjet recording apparatus outputs an automatic shutoff signal in a case where the number of revolutions of the motor falls outside of an allowable range when ink pressure is consistent with a proper value.
In addition, Japanese Patent Application Publication No. 2008-247021 discloses a fluid suction adjustment method of a tube pump which performs suctioning of a head, wherein the method includes storing suction capability information (suction amount, suction rate) of the tube pump and correcting an inherent suction force of the pump based on the suction capability information.
However, since the technique disclosed in Japanese Patent Application Publication No. 2000-229422 measures pressure in a continuous inkjet recording apparatus in a state where ink is being ejected from a head due to feeding of the ink by a pump and therefore measures a pressure value which includes variations in flow channel resistance due to nozzle clogging or the like, it is difficult to describe that an isolated performance of the pump is being accurately measured. On the other hand, when the configuration disclosed in Japanese Patent Application Publication No. 2000-229422 is used to measure a pressure increasing performance of a pump in a state where supply of ink has been stopped by closing a valve between a head and an ink supplying system, an abrupt increase in pressure occurs due to feeding of ink by the pump, which makes it difficult to accurately measure the pressure increasing performance of the pump.
In addition, while the technique disclosed in Japanese Patent Application Publication No. 2008-247021 enables variances in pump performance in an initial state to be corrected, since an isolated suction performance of the pump is measured before the pump is incorporated into an apparatus, a measurement result is stored in an IC chip, and the pump is subsequently controlled based on the suction performance stored in the IC chip, it is difficult to accommodate a change in suction performance over time. Meanwhile, although it is described that a fictitious flow rate is identified by referring to ink suction amount data and an ink suction amount due to driving of a tube pump is computed by multiplying a separately-acquired number of revolutions of the pump with the fictitious flow rate and that it is possible to discern a suction amount of the tube pump in a state where the tube pump is incorporated into an apparatus, the calculated suction amount is a value which includes variations in flow channel resistance due to nozzle clogging or the like. Therefore, it is difficult to describe that an isolated performance of the pump is being accurately discerned.